<!DOCTYPE html>
<html>
<head>
	<title></title>
	<style type="text/css">
	#box{
		border: 1px solid red;height: 100px;width: 100px;
		background-color: red;
	}
</style>
</head>
<body>
	<input type="button" name="" value="Click" id="btn">
	<div id="box"></div>
	<script type="text/javascript">
		var btn = document.getElementById('btn');
		var box = document.getElementById('box');
		btn.onclick = function(){
			if (box.style.display == 'none'){
				box.style.display = 'block';
			}else{
				box.style.display = 'none';
			}
		};
	</script>
</body>
</html>